System for removing minerals from a brine

ABSTRACT

A system includes an ion exchange softener fluidly coupled to a wastewater treatment system. The first ion exchange softener may receive a first brine stream from the wastewater treatment system and to remove a plurality of minerals from the first brine stream to generate a second brine stream including the plurality of minerals and a third brine stream. The system also includes a mineral removal system disposed downstream from the ion exchange softener and that may receive the second brine stream and to generate a sodium chloride (NaCl) brine stream and an acid and caustic production system disposed downstream from and fluidly coupled to the mineral removal system. The acid and caustic production system includes a first electrodialysis (ED) system that may receive the NaCl brine stream from the mineral removal system and to generate hydrochloric acid (HCl) and sodium hydroxide (NaOH) from the NaCl brine stream. The system also includes a second ED system disposed downstream from the ion exchange softener and upstream of the acid and caustic production system. The second ED system is fluidly coupled to the ion exchange softener and to the acid and caustic production system, and the second ED may generate desalinated water from the third brine stream and an ED concentrate stream. The second ED system may direct the ED concentrate stream to the acid and caustic production system.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. Non-Provisional patentapplication Ser. No. 14/552,351, entitled “System for Removing Mineralsfrom a Brine,” filed Nov. 24, 2014, which claim benefits from thepriority of U.S. Provisional Patent Application No. 61/908,318, entitled“System for Removing Minerals from a Brine Using Electrodialysis,” filedNov. 25, 2013. Each of the foregoing is hereby incorporated by referencein its entirety.

BACKGROUND

The subject matter disclosed herein relates generally to mineralextraction and, more particularly, to a system for removing mineralsfrom a brine using electrodialysis.

There are several regions in the United States (e.g., the southwesternUnited States including New Mexico, Southern California, and parts ofTexas) and throughout the world that experience shortages in potablewater supplies due, in part, to the arid climate of these geographiclocales. As water supplies are limited, the need for innovativetechnologies and alternative water supplies for both drinking water andagriculture is important. One method for obtaining an alternative sourceof potable water uses desalination systems to produce the potable water.

The desalination process involves the removal of salts from seawater,agricultural run-off water, and/or brackish ground water brines toproduce potable water. Desalination may use an assortment of filtrationmethods, such as nanofiltration and reverse osmosis, to separate the rawstream into a desalinated water stream and a tailing stream. The tailingstreams may contain various salts and other materials left over afterthe desalination process. Indeed, disposal of the tailing streamsproduced by desalination may result in soil degradation and ground watercontamination. Thus, alternative and innovative uses of the tailingstreams may reduce undesirable results of disposing the tailing streams.

One such alternative use involves processing the tailing stream toremove valuable minerals. In particular, inland brackish water andseawater may be rich in sulfates, magnesium, calcium, and otherminerals. Sulfates, mainly in the form of gypsum, have a variety ofcommercial uses, including, but not limited to building materials (e.g.,drywall or sheetrock), skin creams, shampoos, and dental impressionplasters. In addition, gypsum may be used as a fertilizer and/or soilconditioner in the farming industry. Magnesium may also be extracted inthe form of magnesia (e.g., magnesium oxide) which is used in therefractory industry due to its fireproofing capabilities as well as inthe medical field as an ingredient in laxatives. As the traditionaldeposits for these minerals are depleted, the capacity to extract themfrom alternative sources represents both a valuable commercialopportunity as well as a means for lessening the environmental impactcaused by the disposal of waste streams high in salt content.

Existing procedures for the removal of minerals often exhibitssub-optimal efficiency. For example, evaporation pools require a largearea of land and often produce low purity mixed salts with minimalcommercial value. In addition, a waste mixed salt solid resulting fromthe evaporation process may leach into the ground water supply. Othermethods of extraction involve processing the tailing stream produced inbrackish water or seawater desalination plants. However, current mineralextraction procedures for the tailing stream may not operateefficiently.

As described above, desalination systems may employ one for acombination of nanofiltration and reverse osmosis to facilitate thedesalination and removal process. Following an initial separation of apotable water stream from a tailing stream, the tailing stream may beprocessed further by a mineral removal system. For example, variousprecipitation techniques may be performed that facilitate removal ofdissolved minerals from a solution. However, the high salt concentrationin the tailing stream may increase the solubility of many of thesevaluable minerals and, as a consequence, decrease the efficiency inwhich these minerals may be precipitated. Inadequate removal of theseminerals may have a negative impact on the mineral removal systemitself. For example, incomplete gypsum removal may result in scaling offiltration and/or reverse osmosis membranes, thereby reducing the lifeand permeate flux of these membranes. Frequent replacement and repair ofsuch mineral removal system components, in addition to the sub-optimalextraction efficiency, may result in elevated cost of mineral removalprompting the need for further optimization of the mineral removalsystem.

Furthermore, existing procedures may be inadequate to remove impuritiesfrom minerals. The ineffective removal of such impurities, includingarsenic, boric acid, and silica, may result in undesirable impurities inremoved minerals and decreased productivity of the mineral removal plantdue to membrane scaling. Thus, an improved mineral removal system mayfacilitate higher purity of valuable minerals, decrease impurities,increase efficiency, and increase the life-span of components of themineral removal system.

BRIEF DESCRIPTION

In one embodiment, a system includes an ion exchange softener fluidlycoupled to a wastewater treatment system. The first ion exchangesoftener may receive a first brine stream from the wastewater treatmentsystem and to remove a plurality of minerals from the first brine streamto generate a second brine stream including the plurality of mineralsand a third brine stream. The system also includes a mineral removalsystem disposed downstream from the ion exchange softener and that mayreceive the second brine stream and to generate a sodium chloride (NaCl)brine stream and an acid and caustic production system disposeddownstream from and fluidly coupled to the mineral removal system. Theacid and caustic production system includes a first electrodialysis (ED)system that may receive the NaCl brine stream from the mineral removalsystem and to generate hydrochloric acid (HCl) and sodium hydroxide(NaOH) from the NaCl brine stream. The system also includes a second EDsystem disposed downstream from the ion exchange softener and upstreamof the acid and caustic production system. The second ED system isfluidly coupled to the ion exchange softener and to the acid and causticproduction system, and the second ED may generate desalinated water fromthe third brine stream and an ED concentrate stream. The second EDsystem may direct the ED concentrate stream to the acid and causticproduction system.

In a second embodiment, a method includes directing a wastewater brinestream from a water treatment system to a first ion exchange softenerdisposed upstream of a mineral removal system. The wastewater brinestream includes a plurality of minerals. The method also includesgenerating a first softened brine stream and a first chloride brinestream from the wastewater brine stream via the first ion exchangesoftener. The first chloride brine stream includes a first portion ofthe plurality of minerals and the first softened brine stream includes asecond portion of the plurality of minerals. The method also includessupplying the first chloride brine stream to the mineral removal systemto recover the first portion of the plurality of minerals, supplying thefirst softened brine stream to a first electrodialysis (ED) system thatmay generate a second softened brine stream, and generating hydrochloricacid (HCl) and sodium hydroxide (NaOH) from the second softened brinestream via an acid and caustic production system downstream from andfluidly coupled to the first ED system.

In a third embodiment, a method includes removing a plurality ofminerals from a first brine stream via an ion exchange softener disposedupstream of a mineral removal system. The first brine stream is outputfrom a waste treatment system, the ion exchange softener includes aresin, and the resin includes an acid portion and a neutral portion. Themethod also includes reacting bicarbonate in the first brine stream withthe acid portion of the resin within the ion exchange softener togenerate carbon dioxide, and generating a softened brine stream and asecond brine stream from the first brine stream via the ion exchangesoftener. The second brine stream includes the plurality of minerals andis directed toward the mineral removal system, and the softened brinestream includes the carbon dioxide and is directed toward anelectrodialysis (ED) system that may generate desalinated water.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a block diagram of an embodiment of a water processing system,wherein the water processing system includes a water removal planthaving a mineral removal system and a hydrochloric acid (HCl) and sodiumhydroxide (NaOH) production system, in accordance with aspects of thepresent disclosure;

FIG. 2 is a block diagram of an embodiment of the mineral removal plantof FIG. 1, wherein the mineral removal plant includes an ion exchangesoftener upstream of the mineral removal system, in accordance withaspects of the present disclosure;

FIG. 3 is a block diagram of another embodiment of the mineral removalplant of FIG. 2, illustrating the HCl and NaOH production system, inaccordance with aspects of the present disclosure; and

FIG. 4 is a flow diagram of an embodiment of a method for mineralremoval and production of HCl and NaOH using the water processing systemof FIGS. 1-3, in accordance with aspects of the present disclosure.

DETAILED DESCRIPTION

One or more specific embodiments of the present disclosure will bedescribed below. In an effort to provide a concise description of theseembodiments, all features of an actual implementation may not bedescribed in the specification. It should be appreciated that in thedevelopment of any such actual implementation, as in any engineering ordesign project, numerous implementation-specific decisions must be madeto achieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

When introducing elements of various embodiments of the presentinvention, the articles “a,” “an,” “the,” and “said” are intended tomean that there are one or more of the elements. The terms “comprising,”“including,” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.

As discussed in detail below, the disclosed embodiments include a waterprocessing system (e.g., desalination system) configured to soften highsalinity brine generated during desalination of water (e.g., seawater,agricultural run-off water, and/or brackish ground water). In waterdesalination processes, ion separation systems are used to extractminerals (e.g., calcium, magnesium, sodium, and sulfate) from tailingstreams (e.g., nanofiltration (NF), electrodialysis (ED), and/or reverseosmosis (RO) non-permeate streams) that may otherwise be discarded. Theextracted minerals may be recovered as industrial grade products forcommercial use. The ion separation systems may include one or moreelectrodialysis bipolar membranes (EDBM) that use ion-selectivemembranes to desalinate the water. Ion-selective membranes may becostly, thereby increasing the overall cost of water desalination andmineral removal. Therefore, it may be desirable to reduce a hardness ofthe water upstream of the electrodialysis membranes such that lessexpensive non-ion selective membranes may be used. As such, the overallcost of desalination and mineral removal may be decreased.

FIG. 1 is a block diagram of an embodiment of a water processing system10 that may use non-selective membranes for desalination of water andmineral removal. For example, the water processing system 10 may be partof a water desalination system, wastewater treatment system, waterpurification system, oil and gas brine treating system or any othersuitable water processing system. In the illustrated embodiment, thewater processing system 10 is used to produce desalinated water from afeed stream and to remove minerals from the feed stream. For example,the water processing system 10 may be used to produce high purityagricultural grade gypsum (CaSO.2H₂O) (e.g., approximately greater than97 weight percent (wt %) gypsum on a dry basis), industrial gradecaustic (e.g., approximately greater than 97 wt % sodium hydroxide(NaOH) on a dry basis), industrial grade magnesium hydroxide (Mg(OH)₂)(e.g., approximately greater than 98 wt % Mg(OH)₂ on an ignited basis,or on an ignited oxide basis) suitable for industrial magnesiarefractory, industrial grade sodium chloride (NaCl) (e.g., approximatelygreater than 99.9 wt % NaCl on a dry basis), concentrated HCl forcommercial use (e.g., approximately 10 wt % to approximately 35 wt %HCl), and/or desalinated water (e.g., approximately less than 1.0grams/Liter (g/L) (1000 parts per million (ppm)) total dissolved solids(TDS)) from underground brines, seawater desalination waste brines,and/or brackish water desalination waste brines. Furthermore, the waterprocessing system 10 may use a combination of one or more of gypsumprecipitation, magnesium hydroxide precipitation, electrodialysis (ED),and/or softening and nanofiltration (NF) to remove the minerals frombrines as industrial grade products and/or to substantially reduce (oreliminate) a waste brine stream.

In the illustrated embodiment, the water processing system 10 includes apretreatment system 12 configured to receive a feed stream 14. The feedstream 14 may be received from any suitable water source. For example,the feed stream 14 may be received from ground water, seawater, brackishwater, and so forth. Moreover, the feed stream 14 may contain variouselements and/or compounds. For example, the feed stream 14 may containNaCl, sulfate (SO₄), calcium (Ca), magnesium (Mg), and/or silicondioxide (silica or SiO₂). In certain embodiments, the feed stream 14 maycontain approximately 0.50 g/L (500 ppm) to approximately 3.00 g/L(3,000 ppm) NaCl, approximately 0.10 g/L (100 ppm) to approximately 1.50g/L (1,500 ppm) SO₄, approximately 0.01 g/L (10 ppm) to approximately0.80 g/L (80 ppm) Ca and Mg, and/or approximately 0.01 g/L (10 ppm) toapproximately 0.30 g/L (30 ppm) SiO₂. Furthermore, in certainembodiments, the feed stream 14 may have a pH range betweenapproximately 5 and approximately 9. For example, the feed stream 14 mayhave a pH of approximately 8.

In certain embodiments, the pretreatment system 12 receives the feedstream 14 and removes solid materials (e.g., fines 16), such as iron(Fe) and manganese (Mn), from the feed stream 14. In other embodiments,the iron and manganese may be removed downstream from the pretreatmentsystem 12 (e.g., in a mineral removal system), as discussed in detailbelow. The pretreatment system 12 provides a pretreated feed stream 18to a first reverse osmosis (RO) system 20. The first RO system 20receives the pretreated feed stream 18 and produces a desalinated waterstream 28. In certain embodiments, the desalinated water stream 28 mayinclude SiO₂. Moreover, the desalinated water stream 28 may have a pH ofapproximately 7.5. Furthermore, the first RO system 20 provides a brinestream 30 to a mineral removal system 32. In certain embodiments, thedesalinated water stream 28 may be approximately 70 percent toapproximately 90 percent of the output from the first RO system 20, andthe brine stream 30 may be approximately 10 percent to approximately 30percent of the output from the first RO system 20. For example, in someembodiments, the desalinated water stream 28 may be approximately 80percent of the output from the first RO system 20, and the brine stream30 may be approximately 20 percent of the output from the first ROsystem 20. As may be appreciated, while the illustrated embodiment usesthe first RO system 20, other embodiments may use an NF system in placeof an RO system.

The mineral removal system 32 may be part of a mineral removal plant 34.The mineral removal plant 34 is configured to remove minerals, elements,and/or compounds from the brine stream 30. As may be appreciated, thebrine stream 30 may be provided to the mineral removal plant 34 from anysuitable source and/or system. In certain embodiments, the brine stream30 may include substantial amounts of salts, such as NaCl, sodiumsulfate (Na₂SO₄), calcium (Ca), and/or magnesium (Mg). As discussedabove, softening the brine stream 30 (e.g., reduce an amount of thesalts in the brine stream 30) may mitigate scaling (precipitation) ofthe salts. Accordingly, the system 10 may soften the brine stream 30mechanically (e.g., with an ion exchange system), as discussed infurther detail below. The mineral removal system 32 may provide one ormore desalination streams 36 that include desalinated water (which maycontain SiO₂). Furthermore, the one or more desalination streams 36 mayinclude a disinfectant and/or oxidant. The disinfectant and/or oxidantmay be provided to the pretreatment system 12 via a disinfectant stream38.

A lime based material 40 (e.g., lime, quick lime, dolomitic lime, etc.)may be provided to the mineral removal system 32 to facilitate mineralremoval from the brine stream 30. During operation, the mineral removalsystem 32 may be configured to remove any suitable minerals, elements,and/or compounds from the brine stream 30. For example, the mineralremoval system 32 may provide a gypsum stream 46 (e.g., agriculturalgrade gypsum), a salt stream 50 (e.g., industrial grade sodiumchloride), a magnesium hydroxide stream 54 (e.g., industrial grademagnesium hydroxide), a bromine stream 58, a potash stream 62, and/orother mineral streams depending on the mineral content of the brinestream 30.

The mineral removal system 32 may generate additional streams that maybe collected for commercial use and/or utilized in a downstream processof the water processing system 10. In certain embodiments, the mineralremoval system 32 may provide one or more output streams 64 to an HCland NaOH production system 66. For example, the mineral removal system32 may provide a NaCl brine to the HCl and NaOH production system 66.The HCl and NaOH production system 66 may generate concentrated HCl viaan ion separation process (e.g., ED process) followed by an evaporationprocess. Furthermore, the mineral removal system 32 may receive one ormore input streams 68 from the HCl and NaOH production system 66. Theone or more input streams 68 may provide the mineral removal system 32with HCl and/or caustic (e.g., NaOH) produced by the HCl and NaOHproduction system 66. In addition, the HCl and NaOH production system 66may generate a caustic solution 70 (e.g., NaOH) and/or a concentratedHCl product solution 72 that is not used by the mineral removal system32 (e.g., produced to be sold).

The mineral removal plant 34 also includes a heating and powerproduction system 74. The heating and power production system 74 mayinclude a natural gas engine and/or a boiler. The heating and powerproduction system 74 may be configured to receive a fuel 76. The fuel 76may be any suitable fuel, such as natural gas, synthetic natural gas(e.g., syngas), or combination thereof. The heating and power productionsystem 74 may provide power, steam, hot water, any suitable heatedfluid, and so forth to the HCl and NaOH production system 66, asindicated by arrow 80. Moreover, the heating and power production system74 may receive a cooled fluid stream 82 (e.g., cooled water) from theHCl and NaOH production system 66. As illustrated, the heating and powerproduction system 74 may also provide power to the mineral removalsystem 32, as indicated by arrow 84. Additionally, the heating and powerproduction system 74 may provide power 88 to another system and/or thefirst RO system 20, as indicated by arrow 90.

FIG. 2 is a block diagram of an embodiment of the mineral removal plant32 that may be used with the system 10 to reduce the salinity of thebrine stream 30. As previously described, the mineral removal system 32receives the brine stream 30 from the first RO system 20. As may beappreciated, the brine stream 30 may contain various hardness elementsand/or compounds. For example, the brine stream 30 may contain varioussalts and minerals such as, but not limited to, NaCl, SO₄, Ca, Mg,and/or SiO₂. In certain embodiments, the brine stream 30 may containapproximately 3.0 g/L (3,000 ppm) to approximately 8.0 g/L (8,000 ppm)NaCl, approximately 3.0 g/L (3,000 ppm) to approximately 8.0 g/L (8,000ppm) SO₄, approximately 0.1 g/L (100 ppm) to approximately 0.4 g/L (400ppm) Mg, approximately 0.2 g/L (200 ppm) to approximately 0.6 g/L (600ppm) Ca, and/or approximately 0.05 g/L (50 ppm) to approximately 0.02g/L (200 ppm) SiO₂. Furthermore, in certain embodiments, the brinestream 30 may have a pH range between approximately 4 and approximately8. For example, the brine stream 30 may have a pH of approximately 6.

In the illustrated embodiment, the brine stream 30 flows through a firstion exchange softener 96 (e.g., such as an Amberlite™ IRC747manufactured by The Dow Chemical Company of Midland, Mich.) where asubstantial portion (e.g., approximately greater than 99%) of hardnessminerals are removed. For example, the first ion exchange softener 96removes divalent cations (e.g., Ca²⁺, Mg²⁺, Fe²⁺, Mn²⁺, Sr²⁺, and Ba²⁺)from the brine stream 30, thereby reducing a hardness of the brinestream 30. In operation, a resin within the first ion exchange softener96 absorbs the divalent ions from the brine stream 30 to generate afirst softener effluent stream 98. The first softener effluent stream 98may have approximately less than 0.015 g/L (15 ppm) of Ca, Mg, Sr, andBa. Iron (Fe) and manganese (Mn) in the brine stream 30 are kept in areduced divalent state such that they may be removed as dissolvedspecies without scaling of the softener resin. The brine stream 30 mayalso contain bicarbonate (HCO₃). As discussed below, the first ionexchange softener 96 may convert the bicarbonate to carbon dioxide(CO₂). The carbon dioxide may be removed in an air stripper 100downstream from the first ion exchange softener 96 as CO₂ gas 104,generating a degassed softened brine stream 106. In certain embodiments,multiple stages are used in the air stripper 100 to enable a low CO₂residual (e.g., less than approximately 0.002 g/L (2 ppm) CO₂). A lowCO₂ residual may inhibit carbonate reformation and scaling when a pH ofthe first softener effluent stream 98 increases during the variousdownstream brine treatment steps. The degassed softened brine stream 106is desalinated to generate the desalinated water 28, as discussed indetail below.

Prior to degassing, the first softener effluent 98 may be heated with aheat exchanger 107 to between approximately 32° C. (90° F.) andapproximately 50° C. (122° F.). The heat exchanger 107 may use vacuumvapors from a caustic evaporator within the HCl and NaOH productionsystem 66 to heat the first softener effluent stream 98. In certainembodiments, the first softener effluent stream 98 may be mixed with HCl108 (e.g., between approximately 6 wt % and approximately 8 wt % HCl)upstream of the air stripper 100 and downstream from the heat exchanger107. The HCl 108 may decrease a pH of the first softener effluent stream98 to less than approximately 4, thereby converting any residual HCO₃ toCO₂. As should be noted, the HCl 108 may be generated by the HCl andNaOH production system 66.

During softening of the brine stream 30, the first ion exchange softener96 may become saturated with the divalent ions (e.g., Ca and Mg).Accordingly, the first ion exchange softener 96 may be treated with theHCl 108 to remove the absorbed divalent ions from the softener resin,thereby regenerating the softener resin. Treatment of the first ionexchange softener 96 with the HCl 108 generates a first concentratedbrine stream 110, which includes the hardness and divalent ions (e.g.,Ca²⁺, Mg²⁺, Fe²⁺, Mn²⁺, Sr²⁺, Ba²⁺, and SO₄ ²⁻) and NaCl. The firstconcentrated brine stream 110 is fed to the mineral removal system 32for mineral removal and recovery, as discussed in detail below. Inaddition to adding the HCl 108, the first ion exchange softener 96 maybe treated with NaOH 114 (e.g., between approximately 0.1 wt % andapproximately 4 wt %). The NaOH 114 may neutralize at least a portion ofthe first ion exchange softener 96 after regeneration (e.g., removal ofhardness divalent species) of the softener resin with the HCl 108. Forexample, the NaOH 114 converts a portion of the softener resin from anacid form (H⁺) 116 to a sodium form (Na⁺) 118, thereby neutralizing theportion of the softener resin. Therefore, in certain embodiments, thesoftener resin may be in both the acid and sodium forms 116, 118,respectively. The sodium form 118 of the softener resin may remove thehardness and divalent ion species from the brine stream 30 via ionexchange, while the acid form 116 may convert the bicarbonate in thebrine stream 30 to the CO₂ 104. As such, additional HCl 108 may not needto be added downstream of the first ion exchange softener 96 for removalof the bicarbonate.

A concentration of the NaOH 114 may be adjusted based, at least in part,on an amount of bicarbonate in the brine stream 30. For example, if theconcentration of the bicarbonate in the brine stream 30 is high (e.g.,greater than approximately 200 mg/L (200 ppm)), the concentration of theNaOH 114 may be decreased such that less of the softener resin isneutralized. That is, by adding less concentrated NaOH 114 to the firstion exchange softener 96, less of the acid form 116 of the resin may beneutralized to the sodium form 118. Therefore, more acid may beavailable in the softener resin to convert the bicarbonate to CO₂ inbrine streams having a high concentration of bicarbonate. In contrast,if the bicarbonate concentration is low (e.g., less than approximately50 mg/L (50 ppm)), a higher concentration of NaOH 114 may be used toneutralize a larger portion of the softener resin. Effluent generatedfrom the neutralization of the first ion exchange softener 96 isessentially desalinated water. For example, the sodium ions in the NaOH114 are absorbed by the softener resin and the hydroxide ions (OH⁻) inthe NaOH 114 react with the acid (H⁺) in the softener resin to generatedesalinated water effluent (e.g., the one or more desalinated waterstreams 36). The desalinated water effluent may be combined with thedesalinated water stream 28.

As discussed above, the degassed softened brine stream 106 isdesalinated to produce at least a portion of the desalinated water 28.While the hardness and divalent scale forming compounds/elements areremoved, the degassed softened brine stream 106 may still containimpurities and other scale forming compounds such as silica (SiO₂) andsodium sulfate (Na₂SO₄). Accordingly, the degassed softened brine stream106 is routed to a first nanofiltration (NF) unit 120 that removes oneor more of the other scale producing species (e.g., SO₄) from thedegassed softened brine stream 106. The degassed softened brine stream106 may be mixed with an anti-scalant 124 upstream of the first NF unit120. The anti-scalant 124 may mitigate precipitation of silica in thedegassed softened brine stream 106. Non limiting examples of theanti-scalant include phosphonates such as 1-hydroxyethylidene1,1-diphosphonic acid (HEDP) or other proprietary silica anti-scalantssuch as Vitec 4000 (Avista Technologies Inc) Genesys SI (GenesysInternational Ltd). Additionally, in certain embodiments NaOH 114 may beadded to the degassed softened brine stream 106. The NaOH 114 may adjusta pH of the degassed softened brine stream 106 to above approximately 4.For example, the NaOH 114 may increase the pH of the degassed softenedbrine 106 to between approximately 4 and approximately 7. The pHincrease may cause precipitation of certain compounds within thedegassed softened brine 106. Therefore, the degassed softened brine 106may be filtered before feeding to the first NF unit 120. For example,the degassed softened brine 106 may be filtered through a first filter126. The first filter 126 may remove the precipitated solids (e.g., ironhydroxide) formed during pH adjustment of the degassed softened brine106. In certain embodiments, the first filter 126 may be a 2-8 micronfilter cartridge. However, any other suitable filter size may be used toremove the solids.

The first NF unit 120 may include 2 to 4 stages of reverse osmosis andnanofiltration membranes that remove the sulfate from the degassedsoftened brine stream 106. Accordingly, the first NF unit 120 maygenerate a first NF permeate stream 130 having less than approximately20% sulfate. A first NF non-permeate stream 136 may be routed to themineral removal system 32, as discussed in detail below. The first NFpermeate stream 130 may include approximately 80% or more of silica andchloride, and residual sulfate. Therefore, the first NF permeate stream130 is routed to a first electrodialysis (ED) system 138 for removal ofthe chlorides and residual sulfate, thereby generating the desalinatedwater 28. The desalinated water 28 includes most of the silica (e.g.,greater than approximately 80%) from the brine stream 30.

In addition to having chlorides and residual sulfate, the first NFpermeate stream 130 may also include arsenic (As). For example, thebrine stream 30 may have dissolved arsenic from brackish groundwatertreatment upstream of the mineral removal system 32. The first NF unit120 does not remove the dissolved arsenic. Therefore, to meet drinkingwater standards, the first NF permeate stream 130 may be treated with anoxidizing agent 142, e.g., sodium hypochlorite or other suitableoxidant. In certain embodiments, the oxidizing agent 142 may be added tothe degassed softened brine stream 106 upstream from the first NF system120. The oxidizing agent 142 oxidizes the arsenic and generates arsenate(AsO₄H₃). Depending on the pH of the first NF permeate stream 130, thepH may be adjusted with either HCl 108 or NaOH 114 such that the firstNF permeate stream 130 has a pH of approximately 5. At pH 5, arsenate isin ionic form (e.g., H₂AsO₄ ⁻). Therefore, arsenate, in the ionic form,may be removed by the first ED system 138. An ED concentrate stream 146may be routed to the HCl and NaOH production system 66 where it isseparated into an HCl product stream 108, an NaOH product stream 114, apurge sodium sulfate and sodium chloride brine stream 147 anddesalinated water streams 148 and 150. Stream 150 may be used to dilutethe ED concentrate stream 146, thereby decreasing a concentration ofNaCl and SO₄ in the ED concentrate stream 146. By removing the hardnessand divalent compounds/elements in the brine stream 30 before the stream30 is fed to the NF and ED systems, the ED system 138 may utilizenon-selective membranes to generate the desalinated water streams 36.The non-selective membranes generally have a lower cost compared to ionselective membranes (e.g., monovalent selective membranes). Therefore,the overall operational and maintenance costs of the system 10 may bedecreased, as compared to system that employ ion selective membranesthroughout the system and do not have a softener (e.g., the first ionexchange softener 96).

As discussed above, the mineral removal system 32 receives the firstconcentrated brine stream 110, the first NF non-permeate stream 136, thepurge sodium sulfate and sodium chloride stream 147, and the desalinatedwater stream 148. The mineral removal system 32 removes minerals (e.g.,hardness and divalent compounds/elements, chlorine salts, and sulfate)from the respective streams 110, 136, and 146, thereby generating thegypsum 46, magnesium 54, and other compounds (e.g., salt 50, bromine 58,and potash 62). For example, in the illustrated embodiment, the stream110 is directed to a magnesium hydroxide removal system 154. Duringoperation, the magnesium hydroxide removal system 154 is configured torecover Mg from the brine stream 30 in the form of magnesium hydroxide54. The stream 110 may be treated with caustic (e.g., the NaOH 114) andthe oxidizing agent 142 upstream of the magnesium hydroxide removalsystem 154. The oxidizing agent 142 oxidizes the iron species Fe²⁺ toFe³⁺. The NaOH 114 adjusts a pH of the stream 110 to betweenapproximately 5 and approximately 7, which enables formation andprecipitation of ferric hydroxide (Fe(OH)₃). The ferric hydroxide may beremoved by filtering the stream 110 through a second filter 156.

In certain embodiments, the filtered stream 110 may be treated withadditional caustic to increase the pH to between approximately 8 andapproximately 10, thereby precipitating manganese and generatingindustrial grade manganese. In other embodiments, both the manganese andiron may be precipitated in a single step by adjusting the pH of thestream 110 to between approximately 8 and approximately 10 beforefiltering in the second filter 156. Rather than in a two step process,e.g., first adjusting the pH to between approximately 5 andapproximately 7 to precipitate the ferric hydroxide before filtering thestream 110 in the second filter 156, followed by adjusting the pH tobetween approximately 8 and approximately 10 after filtering the stream110 in the second filter 156 to precipitate manganese.

The second filter 156 may be regenerated periodically by adding HCl 108(e.g., between approximately 5 wt % and approximately 20 wt % HCl). TheHCl 108 dissolves the iron and manganese, thereby regenerating thesecond filter 156. Acidified filter effluent 158 containing thedissolved iron, and, in certain embodiments, manganese, may be fed to agypsum removal system 160. The acidified filter effluent 158 may be usedas a coagulant in the gypsum removal system 160 or may be concentratedand sold as a commercial coagulant. A filtered brine stream 164 isrouted to the magnesium hydroxide removal system 154. While in themagnesium hydroxide removal system 154, the filtered brine stream 164 istreated with the lime 40 or between approximately 7 wt % and 12 wt %caustic (e.g., NaOH 114) from the HCl and NaOH production system 66. Forexample, the filtered brine stream 164 may be treated with lime 40 whena Ca/SO₄ molar ratio in the filtered brine stream 164 is less thanapproximately 1. That is, when a concentration of SO₄ in the filteredbrine stream 164 is more than a concentration of Ca. In contrast, whenthe Ca/SO₄ molar ratio in the filtered brine stream 164 is greater thanapproximately 1, the filtered brine stream 164 may be treated with NaOH114. The lime 40 and NaOH 114 enable precipitation of Mg(OH)₂, therebyrecovering the Mg(OH)₂ 54 (between approximately 50 wt % toapproximately 70 wt % Mg(OH)₂) and from the brine stream 30. The Mg(OH)₂54 recovered may be sold an industrial grade product.

Following magnesium recovery in the magnesium hydroxide removal system154, an effluent brine stream 170 is directed to the gypsum removalsystem 160. The gypsum removal system 160 recovers the Ca and SO₄ fromeffluent brine stream 170 to generate the gypsum 46. In embodiments inwhich the Ca/SO₄ ratio is greater than 1, the effluent brine stream 170may be treated with the HCl 108 (between approximately 6 wt % andapproximately 8 wt % HCl) to adjust a pH of the effluent brine stream170 to between approximately 7 and approximately 8. At least a portionof the pH adjusted effluent brine stream 170 is fed to a second EDsystem 174. The second ED unit 174 may extract a portion of the calciumin the effluent brine stream 170, thereby generating calcium chloride(CaCl₂) brine 178 having between approximately 15 wt % and approximately35 wt % CaCl₂. The CaCl₂ brine 178 may be made available as a commercialproduct. An ED diluate stream 180 containing the remaining calciumchloride and sodium sulfate and sodium chloride brine (stream 212 and238) is fed to the gypsum removal system 160 for removal of Ca and SO₄to generate the gypsum 46.

The gypsum removal system 160 may include a mixer 182, a settler 184,and a third filter 186 that facilitate removal of the gypsum 46 from thebrine stream (e.g., the ED diluate stream 180). In certain embodiments,the stream 180 may be treated with the oxidizing agent 142 to convertany residual arsenic to arsenate, as discussed above, upstream of thegypsum removal system 160. The Ca and SO₄ in the stream 180 react in thegypsum removal system 160 to precipitate the gypsum 46. In certainembodiments, approximately 50% to approximately 70% of the SO₄ isremoved from the stream 180. The presence of gypsum 46 seed crystals inthe mixer 182 (e.g., a turbulent mixer) operating at a neutral pH (e.g.,a pH of approximately 6 to 8) may facilitate gypsum 46 precipitationkinetics, thereby enabling rapid gypsum precipitation. The gypsum 54particles may form a suspension and, therefore, may be well mixed withthe water. Accordingly, while in the mixer 182, the stream 180 may betreated with the acidified filter effluent 158 to coagulate (clump) thegypsum 46 particles, and facilitate separation of the gypsum particlesfrom the water. For example, as discussed above, the acidified filtereffluent 158 includes ferric hydroxide, which may be used as acoagulant.

In addition to gypsum 46 precipitation, insoluble calcium fluoride(CaF₂) may also precipitate in the mixer 182, thereby removing asubstantial portion of the fluoride from the stream 180. As such,fluoride scaling in downstream ED systems may be mitigated. In thesettler 184, the gypsum crystals settle, and the saturated near solidsfree solution is decanted off and filtered by the third filter 186(e.g., a sand filter, a microfilter, an ultrafilter, cartridge filterand so forth) to remove residual gypsum particles. A small amount ofsoftened salt brine 187 is recycled to the settler overflow to increasegypsum solubility and to desaturate the brine stream, thereby reducingscaling in the third filter 186 and other downstream units. The settlerbottoms may be routed to a hydroclone and the third filter 186 to wash(e.g., with desalinated product water) and concentrate the gypsum 46into a saleable washed filter cake. In certain embodiments, the filtercake may include approximately 70 wt % to approximately 100 wt % gypsum46. For example, the filter cake may include approximately 90 wt %gypsum 46. Thus, gypsum 46 is provided as an output 188 from the gypsumremoval system 160. The fine solids overflow stream from the hydrocloneis recycled to the mixer 182 as seed crystals. The filtrate from thethird filter 186 is recycled to the settler 184. In certain embodiments,filtrate from the third filter 186 and effluent from the settler 184 aretreated with sodium bisulfate (NaHSO₄) to remove any residual oxidizingagent 142. For example, the NaHSO₄ may react with sodium hypochlorite toproduce SO₄ and chloride.

The gypsum removal system 160 may remove approximately 60% toapproximately 75% of the calcium received from the stream 180 as gypsum46, and produce a NaCl brine stream 190. The NaCl brine stream 190 alsoincludes the SO₄ and chloride generated during treatment of the filtratefrom the third filter 186 and the effluent from the settler 184 withNaHSO₄. The NaCl brine stream 190 may also include residual magnesiumand calcium that were not removed in the removal systems 154, 160. Forexample, the NaCl brine stream 190 may contain less than approximately5-9 g/L (5,000-9,000 ppm) gypsum 54 and less than approximately 0.4 g/L(400 ppm) magnesium chloride. Therefore, the brine stream 190 is fed toa second ion exchange softener 192 before routing to an anti-scalantrecovery ED system 198 within the mineral removal system 32. Similar tothe first ion exchange softener 96, the second ion exchange softener 192removes the residual magnesium and calcium from the brine stream 190,thereby generating a second softener effluent stream 200. In this way,ion selective electrodialysis membranes generally used in ED systems maybe replace with more cost efficient non-selective electrodialysismembranes. The second ion exchange softener 192 is treated with HCl 108and NaOH 114, and a second concentrated brine stream 202 is produced andcombined with the stream 164 downstream from the second filter 156 tofacilitate recovery of the calcium and magnesium.

The second softener effluent stream 200 and the purge sodium sulfate andsodium chloride stream 147 from the HCl and NaOH production system 66 isdirected to a second NF system 206. The second NF system 206 enablesremoval of sulfate from the second softener effluent stream 200, andgenerates a second NF permeate stream 210 (e.g., having greater thanapproximately 40 g/L (40,000 ppm) NaCl) and a second NF non-permeatestream 212. The second NF non-permeate stream 212 may include betweenapproximately 50 g/L (50,000 ppm) and approximately 70 g/L (70,000 ppm)total dissolved solids, which include Ca and SO₄. Therefore, the secondNF non-permeate stream 212 is directed to the gypsum removal system 160to recover the Ca and SO₄ as the gypsum 46. In certain embodiments, thesecond softener effluent stream 200 may be combined with the first NFnon-permeate stream 136 upstream of the second NF system 206. Thestreams 136, 200 may be neutralized with HCl 108 (between approximately5 wt % and approximately 8 wt % HCl) and filtered with a fourth filter214 (similar to the filters 126, 156) before being fed to the second NFsystem 206. The fourth filter 214 may substantially block gypsum scalefrom passing to the second NF system 206. In certain embodiments, aportion of the second softener effluent stream 200 may be recycled tothe gypsum settler 184. The recycled brine may desaturate effluent fromthe settler 184 and reduce gypsum scaling in the gypsum recovery system160.

In addition to having a high concentration of NaCl, the second softenereffluent stream 200 also includes the anti-scalant 124. It may bedesirable to recover and recycle the anti-scalant 124 used throughoutthe system 10. Recovering and recycling the anti-scalant 124 maydecrease the overall operational costs of the system 10 by decreasingcosts associated with the purchase of the anti-scalant 124. Accordinglya portion of the second softener effluent stream 200, the second NFpermeate stream 210, and desalinated water stream 148 is routed to theanti-scalant recovery ED system 198 for recovery of the anti-scalant124. In the illustrated embodiment, the anti-scalant recovery ED system198 includes a first stage ED unit 218, a second stage ED unit 220, anda third stage ED unit 224. However, as should be appreciated, theanti-scalant recovery ED system 198 may include more or fewer stages.For example, the anti-scalant recovery ED system 198 may include one,two, three, four, five, or more ED stages. The ED units 218, 220, and224 may use cation and anion selective membranes or non-selectivemembranes for removal of residual arsenate, calcium, and magnesium fromthe second NF permeate stream 210. For example, the second NF permeatestream 210 is fed to a concentrate side of the first stage ED unit 218,and a portion 225 of the softener effluent stream 200 is fed to adiluate side of the first stage ED unit 218. The first stage ED unit 218extracts sodium chloride (NaCl) and residual arsenate from the portion225 of the softener effluent stream 200 into the second NF permeatestream 210. The first stage ED unit 218 may operate at a pH ofapproximately 4 to approximately 7. The higher pH enables ionization ofthe arsenic to generate arsenate, thereby facilitating removal ofarsenic from the second NF permeate stream 210. At the operational pH ofthe first stage ED unit 218, silica in the second NF permeate stream 210is non-ionic. Therefore, the first stage ED unit 218 may not removesilica. As such, a first stage ED concentrate stream 226 may includeapproximately less than 0.01 g/L (100 ppm) silica.

A first stage ED diluate stream 228 having the anti-scalant 124 is fedto the second stage ED unit 220. The first stage ED concentrate stream226 is directed to the HCl and NaOH production system 66 and used forproduction of HCl and NaOH (e.g., the HCl 72, 108 and NaOH 114), asdiscussed in detail below with reference to FIG. 3. In certainembodiments, a pH of the first stage ED diluate stream 228 may beadjusted by adding HCl 108 (between approximately 6 wt % andapproximately 8 wt % HCl). For example, the pH of the first stage EDdiluate stream 228 may be decreased to less than approximately 3. Inthis way, ferric chloride (Fe(III)Cl₂) added upstream of the secondsoftener 192 may be released from the anti-scalant 124, and theanti-scalant 124 may be recovered in the third stage ED unit 224.

The first stage ED diluate stream 228 includes chloride salts such as,but not limited to, calcium chloride, magnesium chloride, iron chloride,and others. The second stage ED unit 220 (e.g., mixed chlorideextraction ED) extracts a substantial portion (e.g., approximately 65%to 80%) of the magnesium chloride, calcium chloride, and sodium chloridefrom the first stage ED diluate stream 228 using anionic monovalentpermselective membranes to produce a second stage ED dilute stream 230and a second stage ED concentrate stream 234. The stream 234 isconcentrated with magnesium chloride, calcium chloride, and sodiumchloride brine (e.g., approximately 3 wt % to approximately 25 wt %).The second stage ED concentrate stream 234 may be combined with thefirst concentrated brine stream 110 and recycled back through theremoval systems 154, 160. Because the second stage ED diluate stream 230may have an increased concentration of calcium and magnesium, makeupwater from the HCl and NaOH production system 66 may be fed to thesecond stage ED unit 220, as indicated by arrow 148, to dilute the firststage ED concentrate stream 226 and mitigate scaling in the systems 154,160.

The third stage ED unit 224 receives the second stage ED diluate stream230 and uses non-selective membranes to remove residual Na₂SO₄ from thesecond stage ED diluate stream 230 and recover the anti-scalant 124.Similar to the second stage ED unit 220, the third stage ED unit 224 mayalso receive makeup water 148 from the HCl and NaOH production system 66to dilute sodium sulfate brine 238 output from the third stage ED unit224. The third stage ED unit 224 directs the sodium sulfate brine 238 tothe gypsum removal system 160. The third ED unit 224 also generates aregenerated anti-scalant stream 240. The regenerated anti-scalant stream240 may be directed to various streams and/or components of the system10 such that the anti-scalant 124 may be re-used by the system 10 (e.g.,in the NF systems 126, 206). In certain embodiments, the regeneratedanti-scalant 124 may be provided as an industrial grade commercialproduct.

FIG. 3 is an embodiment of the HCl and NaOH production system 66 thatmay be used by the mineral removal plant 34 to generate HCl and NaOH(e.g., the HCl 72, 108 and NaOH 114). As discussed above, the HCl andNaOH production system 66 receives the streams 146, 226 from the EDsystems 138, 198. The HCl and NaOH production system 66 includes a firstabsorber 250 that receives the ED concentrate stream 146. As discussedabove, the ED concentrate stream 146 includes arsenic. The firstabsorber 250 may remove arsenic from the ED concentrate stream 146.Prior to feeding the ED concentrate stream 146 to the first absorber250, the stream 146 may be treated with sodium bisulfate (NaHSO₃). Thesodium bisulfate reacts with residual oxidizing agent 142 used tooxidize arsenic upstream of the first NF system 120. For example, thereaction of sodium bisulfate and the residual oxidizing agent 142 (e.g.,sodium hypochlorite) produces non-oxidizing chloride and sulfatespecies, thereby blocking oxidation of downstream ion exchange resinsand membranes by residual oxidizing agent 142. The first absorber 250may use disposable single-use absorbents (e.g., for low arsenic contentbrines) or regenerable absorbents (e.g., for high arsenic contentbrines). In embodiments, in which the first absorber 250 usesregenerable absorbents, the absorbent may be periodically regeneratedwith the NaOH 114 and NaCl brine (e.g., from the first stage EDconcentrate 228). A first arsenic-rich stream 254 may be mixed with aferric chloride solution (FeCl₃) to generate ferric arsenate. The ferricarsenate may be removed from the first arsenic-rich brine stream 254with a fifth filter 256, thereby generating a filtered arsenic leanstream 258. The filtered arsenic lean stream 258 is greater thanapproximately 98% NaCl. The filtered arsenic lean stream 258 is recycledback through the first absorber 250, which removes additional arsenicfrom the regenerable absorbent.

A first concentrated brine stream 262 from the absorber 250 is fed to athird NF system 264, which removes greater than approximately 90%residual sulfate, greater than approximately 75% residual calcium andmagnesium, and less than approximately 25% of chloride from the firstconcentrated brine stream 262. The third NF system 264 may include atleast 2 NF stages. A third NF permeate stream 268 is fed to a second ROsystem 270 (e.g., seawater RO system) and a third NF non-permeate stream274 is directed to the mineral removal system 32. The third NFnon-permeate stream 274 includes the residual sulfate, calcium,magnesium, and chloride from the ED concentrate stream 146, which arerecovered as gypsum 46 and Mg(OH)₂ 54 in the mineral removal system 32.In certain embodiments, the third NF non-permeate stream 274 is mixedwith the second softener effluent stream 200 upstream of the second NFsystem 206. In other embodiments, the third NF non-permeate 274 is fedto the anti-scalant recovery ED system 198.

The third NF permeate stream 268 has a low sulfate content (e.g.,approximately 0.1-0.5 g/L (100-500 ppm)) and more than approximately 3%chloride (e.g., approximately 40 g/L (40,000 ppm) to 60 g/L (60,000 ppm)NaCl). As such, the NF permeate stream 268 may be used to produce theHCl 72, 108 and the NaOH 70, 114. For example, the second RO system 270separates the third NF permeate stream 268 into a second concentrated ROpermeate stream 276 (e.g., having between approximately 75 g/L (75,000ppm) and approximately 115 g/L (115,000 ppm) NaCl) and a second ROpermeate stream 278 (e.g., having less than approximately 1 g/L (1000ppm) NaCl low salinity stream). The NaCl in the second RO concentratedbrine stream 276 is high purity NaCl having greater than approximately99 wt % NaCl. Therefore, the second RO concentrated brine stream 276 maybe used to generate NSF 60 certified caustic (e.g., the NaOH 70, 114)and HCl (e.g., the HCl 72, 108), according to the National SanitationFoundation (NSF) Standard 60 (NSF 60). Because the system 10 isconfigured to generate NSF 60 certified NaOH and HCl during operation,costs associated with the purchase of NSF 60 certified NaOH and HCl maybe reduced.

The second RO permeate stream 278 may be used as makeup water (e.g.,makeup water 148, 150) for several processes within the system 10. Forexample, in one embodiment, the second RO permeate stream 278 may be fedto the anti-scalant recovery ED system 198 (e.g., the second and thirdstage ED units 220 and 224), as illustrated by arrow 148. In certainembodiments, the second RO permeate stream 278 may be fed to the firstED system 138, as illustrated by arrow 150. In addition, the second ROpermeate stream 278 may be fed to both the ED systems 138, 198. Thesecond RO permeate stream 278 may also be used as cooling tower makeupand other non-potable water uses (e.g., wash water, irrigation, etc.).

The HCl and NaOH production system 66 also includes several EDBM units280, 282, and 284 (e.g., Electromat Electrodialysis and BipolarElectrodialysis manufactured by GE Power and Water of Trevose, Pa.) thatenable production of the HCl 72, 108 and NaOH 70. The EDBM units 280,282, and 284 may be three cell membranes including a brine compartment290, an acid compartment 292, and a caustic compartment 294. In theillustrated embodiment, the EDBM unit 280 receives the second ROconcentrated permeate stream 276 from the second RO system 270. Inaddition to receiving the second RO concentrated permeate stream 276,the EDBM unit 280 also receives makeup HCl 298 (having approximately 0.5wt % to approximately 4 wt % HCl) and makeup NaOH 300 (havingapproximately 0.5 wt % to approximately 4 wt % NaOH) from the EDBM unit282 (e.g., makeup EDBM) to facilitate production of the HCl 108 and NaOH114. Within the EDBM unit 280 (e.g., export EDBM), chloride is extractedfrom the second RO concentrated permeate stream 276 to produce a firstHCl stream 302 (e.g., approximately 4 wt % to approximately 7 wt % HCl)and a first NaOH stream 304 (e.g., approximately 5 wt % to 12 wt %NaOH). The first HCl stream 302 is fed to an HCl evaporator 308 and theNaOH stream 304 is fed to an NaOH evaporator 310 (e.g., a vacuumevaporator). A first EDBM brine stream 314 may be combined with thefirst concentrated brine stream 262 to mitigate buildup of residualsulfate.

The evaporators 308, 310 concentrate the first HCl stream 302 and thefirst NaOH stream 304, respectively, thereby generating the industrialgrade HCl 72 (between approximately 15 wt % to approximately 20 wt %HCl) and the industrial grade NaOH 70 (between approximately 30 wt % andapproximately 50 wt % NaOH). As should be noted, at least a portion ofthe first HCl stream 302 and the first NaOH stream 302 may be used toprovide the HCl 108 and NaOH 114, respectively, to the various streamsand components of the system 10. In certain embodiments, the HClevaporator 308 is a mechanical vapor recompression (MVR) evaporatorsystem. The MVR evaporator system includes a condenser and a compressor.During concentration of the first HCl stream 302, the HCl evaporator 308generates water vapor. The water vapor and HCl may form an azeotrope,resulting in the presence of HCl in the water vapor. Therefore, aportion of the makeup water 150 from the second RO system 270 may be fedto the HCl evaporator 308, as illustrated by arrow 316. The portion ofthe makeup water 316 may be used as scrubbing water for removal of HClfrom the water vapor. Removing HCl from the water vapor may mitigateundesirable effects of HCl on other components of the evaporator 308(e.g., the compressor). In certain embodiments, spent scrubbing water318 (having approximately less than 1 wt % HCl) may be routed to theacid compartment 292 of the EDBM 284 and used as makeup acid for theproduction of a second HCl stream 320. The second HCl stream 320 may befed to the acid compartment 292 of the EDBM 282, thereby facilitatingproduction of the makeup HCl 298 provided to the EDBM 280. In otherembodiments, the spent scrubbing water 318 may form part of the HCl 108.

Similar to the HCl evaporator 308, the NaOH evaporator 310 (e.g., avacuum evaporator) generates a water vapor stream 326 duringconcentration of the first NaOH stream 310. The water vapor stream 326may be fed to the heat exchanger 107 to heat the first softener effluentstream 98 upstream of the stripper 100. After transferring heat in theheat exchanger 107, the condensed water vapor may be fed to the EDBM 280as makeup water.

As discussed above, the first stage ED concentrated stream 228 is routedto the HCl and NaOH production system 66 to facilitate production of theHCl 72, 108 and NaOH 70, 114. The first stage ED concentrated stream 228may have a large amount of NaCl (e.g. between approximately 30 g/L(30,000 ppm) and approximately 60 g/L (60,000 ppm) NaCl), which may beused by the EDBM units 280, 282, and 284 to generated HCl and NaOH.Accordingly, the first stage ED concentrated stream 228 may be fed tothe brine compartment 290 of the EDBM unit 282. The EDBM unit 282 mayuse the first stage ED concentrated stream 228 to generate the HClmakeup 298 and NaOH makeup 300 fed to the respective compartments 292,294 of the EDBM unit 280. However, prior to feeding the first stage EDconcentrated stream 228 to the EDBM unit 282, the first stage EDconcentrated stream 228 may be treated with the oxidizing agent 142 toionize arsenate and enable removal of the arsenate in a second absorber330. The second absorber 330 operates similarly to the first absorber250 discussed above. The second absorber 330 may operate at a pH ofbetween approximately 5 and approximately 6. The pH in the secondabsorber in combination with a residence time of between approximately 1minute and approximately 5 minutes may minimize co-absorption of silica(approximately 0.01 g/L (100 ppm) silica) in the stream 228. In certainembodiments, the stream 228 may be treated with sodium bisulfate(NaHSO₄) to remove residual oxidizing agent 142 before removal of thearsenic in the second absorber 330. A second arsenic-rich stream 334 iscombined with the first arsenic-rich stream 254 and fed to the fifthfilter 256 to generate the arsenic-lean stream 258, as discussed above.A third concentrated brine stream 336 is fed to the EDBM unit 282,thereby generating the HCl and NaOH makeup streams 306 and 308,respectively, and a second EDBM brine stream 338. The sections 292, 294of the EDBM unit 282 also receive a third HCl stream 240 from the EDBMunit 284 and a mixture of the second RO permeate stream 278 (makeupwater), as illustrated by arrow 342, and caustic condensate from theNaOH evaporator 304, respectively.

The second EDBM brine stream 338 (having between approximately 15 g/L(15,000 ppm) and approximately 50 g/L (50,000 ppm) NaCl) is fed to theEDBM unit 284 (e.g., an internal NaOH consumption EDBM). Additionally,the acid compartment 292 of the EDBM unit 284 receives the spentscrubbing water 318 from the HCl evaporator 308 to enable production ofthe third HCl stream 240. The caustic compartment 294 of the EDBM unit284 is fed a third EDBM brine stream 350 generated in the brinecompartment 290 of the EDBM 284. The third EDBM brine stream 350 mayhave less than approximately 5 g/L (5,000 ppm) NaCl, and enablesproduction of the NaOH 114 used to regenerate the softeners 96, 192 andto adjust the pH of various streams within the system 10.

Present embodiments also include a method that utilizes the first ionexchange softener 96 to remove hardness and divalent elements/compoundsfrom the brine stream 30 upstream of the first NF unit 120 and themineral removal system 32. The HCl and NaOH production system 66 mayfeed HCl and NaOH to regenerate the first ion exchange softener 96 andenable recovery of the hardness and divalent elements/compounds. In thisway, the operational costs of the system 10 may be decreased due, inpart, to the use of less expensive non-selective membranes in the EDsystems 138, 198 (compared to higher cost ion selective membranes),recovery of the anti-scalant 124, and production of NSF 60 certified HCland NaOH (e.g., HCl 72, 108 and NaOH 70, 114). FIG. 4 is a flow diagramof a method 360 by which a wastewater treatment system (e.g., thewastewater treatment system 10 described above) may remove hardness anddivalent elements from a brine stream (e.g., the brine stream 30),recover anti-scalant (e.g., the anti-scalant 124), and generate HCl andNaOH (e.g., the HCl 72, 108 and NaOH 70, 114). In certain embodiments,the first RO system 20 supplies the first ion exchange softener 96 withthe brine stream 30 to generated the first softener effluent stream 98and the concentrated chloride brine stream 106 (block 362), as describedabove with reference to FIG. 2. The first ion exchange softener 96removes Ca, Mg, Fe, Mn, Sr, Ba and other hardness compounds from thebrine stream 30. In addition, the first ion exchange softener 96converts bicarbonate to CO₂. Therefore the amount of HCl 108 used in thesystem 10 may be decreased. For example, in general, the brine stream 30is treated with HCl to convert the bicarbonate to CO₂. However, becausethe first ion exchange softener 96 is configured to convert thebicarbonate to CO₂, the brine stream 30 may not need to be treated withHCl, thereby reducing HCl usage.

The method 360 also includes treating the first softener effluent stream98 with the anti-scalant 124 (block 364) and directing the firstsoftener effluent stream 98 to the first NF system 120 and the first EDsystem 138 to generate desalinated water 28 and the ED concentratestream 146 (block 368). In certain embodiments, the first softenereffluent stream 98 includes silica (SiO₂) that may cause scaling duringdesalination of the first softener effluent stream 98 in the NF system120. Therefore, the first softener effluent stream 98 may be treatedwith the anti-scalant 124 to mitigate scaling. The first NF system 120removes sulfate (SO₄) from the first softener effluent stream 98, andthe first ED system 138 removes greater than approximately 95% of NaClfrom the first softener effluent stream 98, thereby generating thedesalinated water 28 and the ED concentrate stream 146 (NaCl brine).Because most of the hardness and divalent compounds (e.g., greater thanapproximately 98%) are removed in the first ion exchange softener 96,the first ED system 138 may use less expensive non-selective membranesto desalinate the water (e.g., from the brine stream 30)

The method 360 further includes feeding the first concentrated brinestream 110 to the mineral removal system 32 and recovering the hardnessand divalent elements/compounds (block 372). For example, the firstconcentrated brine stream 110 is fed to the magnesium hydroxide removalsystem 154 to recover the magnesium from the first concentrated brinestream 110, thereby generating the magnesium hydroxide 54. Overflow fromthe magnesium hydroxide removal system 154 is fed to the gypsum recoverysystem 160 to recover calcium and sulfate, thereby producing the gypsum46. The magnesium hydroxide 54 and the gypsum 46 may be sold asindustrial grade products.

The method 360 also includes supplying the first NF non-permeate stream136 to the mineral removal system 32 and recovering the anti-scalant 124to generate a NaCl brine (e.g., the first stage ED concentrate stream226) (block 374). The recovered anti-scalant 124 may be recirculatedthroughout the system 10, thereby decreasing costs associated with thepurchase of the anti-scalant 124. In certain embodiments, theanti-scalant 124 may be sold as an industrial grade anti-scalant.

The method 360 also includes supplying NaCl brine streams (e.g., the EDconcentrate stream 146 and the first stage ED concentrate stream 226)from the first ED system 138 and the anti-scalant recovery ED system 198to the HCl and NaOH production system 66 to generate HCl and NaOH (e.g.,HCl 72, 108 and NaOH 70, 114) (block 378). For example, the HCl and NaOHproduction system 66 includes the systems 264, 274 and EDBM units 280,282, 284 that facilitate production of the HCl, 72, 108 and NaOH 70,114, as discussed above with reference to FIG. 3. The HCl 72, 108 andNaOH 70, 114 generated by the HCl and NaOH production system 66 are NSF60 certified quality. The produced HCl and NaOH may be recirculatedthroughout the system 10 (e.g., the HCl 108 and NaOH 114) and/or may besold as high purity industrial grade HCl 72 and NaOH 70. Because thesystem 10 may use the HCl 108 and NaOH 114 generated by the HCl and NaOHproduction system 66, costs associated with the purchase of NSF 60certified HCl and NaOH may be reduced.

The method 360 further includes directing the HCl 108 and NaOH 114 tothe softeners 96, 192 to generate the first concentrated brine stream110 and to regenerate the softeners 96, 192. In this way, the system 10may continue to remove and recover the hardness and divalent compoundsas industrial grade products.

As described above, certain embodiments of the water processing system10 use ion exchange softeners (e.g., the softeners 96, 192) to generatesoftener effluent streams (e.g., streams 98, 200) upstream ofnanofiltration and electrodialysis systems. In this way, hardness anddivalent ions may be removed from brine streams before nanofiltrationand electrodialysis, thereby enabling the use of lower costnon-selective membranes in the electrodialysis systems (e.g., the EDsystems 138, 198). Moreover, the ion exchange softeners 96, 192 mayconvert bicarbonate in the brine stream (e.g., the brine stream 30) toCO₂, thereby decreasing an amount of HCl used by the system 10 toconvert the bicarbonate to CO₂ 104. Additionally, the water processingsystem 10 may recover and recycle anti-scalant (e.g., the anti-scalant124) and generate NSF certified HCl and NaOH. Therefore, costsassociated with the purchase of anti-scalant, HCl, and NaOH may bereduced. Accordingly, the total operation cost of the system 10 may alsobe reduced.

While only certain features of the disclosure have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the present disclosure.

The invention claimed is:
 1. A system, comprising: an ion exchangesoftener fluidly coupled to a wastewater treatment system, wherein theion exchange softener is configured to receive a first brine stream fromthe wastewater treatment system and to remove a plurality of mineralsfrom the first brine stream to generate a second brine stream and athird brine stream, wherein the second brine stream comprises theplurality of minerals; a mineral removal system disposed downstream fromthe ion exchange softener and configured to receive the second brinestream and to generate a sodium chloride (NaCl) brine stream; an acidand caustic production system disposed downstream from and fluidlycoupled to the mineral removal system, wherein the acid and causticproduction system comprises a first electrodialysis (ED) systemconfigured to receive the NaCl brine stream via a first conduit from themineral removal system and to generate hydrochloric acid (HCl) andsodium hydroxide (NaOH) from the NaCl brine stream; and a second EDsystem disposed downstream from the ion exchange softener and upstreamof the acid and caustic production system, wherein the second ED systemis fluidly coupled to the ion exchange softener and to the acid andcaustic production system, the second ED system is configured togenerate desalinated water from the third brine stream, the second EDsystem is configured to generate an ED concentrate stream from the thirdbrine stream, the second ED system is configured to direct the EDconcentrate stream to the acid and caustic production system, and theacid and caustic production system is configured to receive the EDconcentrate stream via a second conduit.
 2. The system of claim 1,comprising an anti-scalant recovery system within the mineral removalsystem, wherein the anti-scalant recovery system is configured togenerate the NaCl brine stream.
 3. The system of claim 2, wherein theanti-scalant recovery system comprises a plurality of ED units.
 4. Thesystem of claim 2, wherein the anti-scalant recovery system is fluidlycoupled to the first ED system and configured to feed the NaCl brinestream to the first ED system.
 5. The system of claim 1, comprising ananofiltration (NF) system disposed downstream from the ion exchangesoftener, wherein the NF system is fluidly coupled to the ion exchangesoftener, the second ED system, and an anti-scalant recovery system, andwherein the NF system is configured to direct an NF non-permeate streamto the anti-scalant recovery system to generate the NaCl brine streamfrom the third brine stream, and the NF system is configured to generatean NF permeate stream from the third brine stream, and wherein the NFsystem is configured to direct the NF permeate stream to the second EDsystem to generate the desalinated water and the ED concentrate stream.6. The system of claim 1, wherein the second ED system comprises anon-selective membrane.
 7. The system of claim 1, wherein the ionexchange softener comprises a resin, the resin comprises an acid portionand a neutral portion, and the acid portion is configured to removebicarbonate from the first brine stream.
 8. The system of claim 1,comprising a first mineral removal section disposed within the mineralremoval system, wherein the first mineral removal section is fluidlycoupled to the ion exchange softener and configured to receive thesecond brine stream, and wherein the first mineral removal section isconfigured to remove a first portion of the plurality of minerals fromthe second brine stream to generate a fourth brine stream comprising asecond portion of the plurality of minerals, and the first mineralremoval section comprises a magnesium hydroxide removal section.
 9. Thesystem of claim 8, comprising a second mineral removal section withinthe mineral removal system, wherein the second mineral removal sectionis configured to remove the second portion of the plurality of mineralsfrom the fourth brine stream, and the second mineral removal sectioncomprises a gypsum removal section.
 10. A system, comprising: an ionexchange softener fluidly coupled to a wastewater treatment system,wherein the ion exchange softener is configured to receive a first brinestream from the wastewater treatment system and to remove a plurality ofminerals from the first brine stream to generate a second brine streamand a third brine stream, wherein the second brine stream comprises theplurality of minerals; a mineral removal system disposed downstream fromthe ion exchange softener, wherein a portion of the mineral removalsystem is configured to receive the second brine stream and to generatea first sodium chloride (NaCl) brine stream; a nanofiltration (NF)system within the mineral removal system, wherein the NF system isconfigured to remove a sulfate from the first NaCl brine stream togenerate a second NaCl brine stream; and an anti-scalant recovery systemwithin the mineral removal system, wherein the anti-scalant recoverysystem is configured to remove anti-scalant from the second NaCl brinestream to generate an anti-scalant stream and a third NaCl brine stream,and the anti-scalant recovery system comprises at least oneelectrodialysis (ED) system.
 11. The system of claim 10, wherein the atleast one ED system comprises a plurality of ED systems.
 12. The systemof claim 10, comprising an acid and caustic production system disposeddownstream from the mineral removal system, wherein the acid and causticproduction system comprises a second ED system configured to receive thethird NaCl brine stream from the anti-scalant recovery system and togenerate hydrochloric acid (HCl) and sodium hydroxide (NaOH) from thethird NaCl brine stream.
 13. The system of claim 12, wherein theanti-scalant recovery system is configured to receive a makeup waterstream from the acid and caustic production system and to generate theanti-scalant stream using the makeup water stream.
 14. The system ofclaim 10, wherein anti-scalant recovery system is configured to directthe anti-scalant stream into the third brine stream to generate atreated third brine stream.
 15. A system, comprising: an ion exchangesoftener fluidly coupled to a wastewater treatment system, wherein theion exchange softener is configured to receive a first brine stream fromthe wastewater treatment system and to remove a plurality of mineralsfrom the first brine stream to generate a second brine stream and athird brine stream, wherein the second brine stream comprises theplurality of minerals, and the ion exchange softener is configured tooutput the second brine stream to a mineral removal system via a firstconduit; a nanofiltration (NF) system fluidly coupled to the ionexchange softener, wherein the NF system is configured to receive thethird brine stream via a second conduit, and the NF system is configuredto generate an NF permeate stream and an NF non-permeate stream; a firstelectrodialysis (ED) system fluidly coupled to the NF system, whereinthe first ED system is configured to receive the NF permeate stream andto generate desalinated water and a sodium chloride (NaCl) brine streamfrom the NF permeate stream, and the first ED system is not directlyfluidly coupled to the mineral removal system; and an acid and causticproduction system disposed downstream from and fluidly coupled to thefirst ED system, wherein the acid and caustic production systemcomprises a second ED system configured to receive the NaCl brine streamfrom the first ED system and to generate hydrochloric acid (HCl) andsodium hydroxide (NaOH) from the NaCl brine stream.
 16. The system ofclaim 15, comprising the mineral removal system disposed downstream fromthe ion exchange softener, wherein a portion of the mineral removalsystem is configured to receive the second brine stream and to generatea second NaCl brine stream.
 17. The system of claim 16, wherein themineral removal system comprises an anti-scalant recovery system, andthe anti-scalant recovery system is configured to generate ananti-scalant stream from the second NaCl brine stream.
 18. The system ofclaim 16, wherein the ion exchange softener is fluidly coupled to theacid and caustic production system, and the ion exchange softener isconfigured to receive the HCl and the NaOH to regenerate the ionexchange softener.
 19. The system of claim 15, wherein the first EDsystem comprises a non-selective membrane.